Los Angeles County social workers took to the picket lines on Thursday, the first county strike in more than a decade and a sharp escalation of a labor dispute between the county and its biggest employee union.

The strike, which may include up to 3,600 social workers and their supervisors, was called Wednesday night by the Service Employees International Union Local 721, which represents more than 55,000 county employees who have been working without a contract for more than two months.

The action could spread beyond social workers because all SEIU members are being urged to respect picket lines.

The two main obstacles in contract negotations are the timing of a pay raise and caseloads for social workers.

At a Compton child-welfare office with one of the heaviest caseloads, strikers protested for relief for overburdened workers and pay raises. A few dozen workers waved signs that read "Families First" and "Child Safety Now!"

Gerson Salazar, 40, is a dependency investigator who said his caseload is 67 children, which hampers his ability to do his job.

"We don't have enough manpower to thoroughly investigate the cases," he said, adding that he routinely deals with families struggling with mental health and substance abuse issues. "They're extremely complicated cases and you can't resolve these issues in two weeks with [the size of our] workforce and be competent."

"That's my main concern; but also raises, fair wages and a better work environment."

He said he was disappointed to see many of his coworkers crossing the picket line. The employee parking lot was full outside the building, where a few hundred people work.

"It's shameful," he said. "They're up there worried about their Christmas ham. Shame on them. This office is full of people."

At a Department of Children and Family Services office on Vermont Avenue in South Los Angeles, several dozen workers walked the perimeter of the building blowing whistles and carrying signs.

Sonny Montoya, 28, an emergency response worker who investigates child abuse allegations, said, "It's not about the money, but how can we take care of others if we can't take care of ourselves?"

Almira Garza, 47, an emergency response worker and union steward who has been with the department for 13 years, said she works as much as 25 hours of overtime a week, often unpaid. She called on the county Board of Supervisors to act to reduce case loads.

"They're passing the buck back and forth from our director to the board of supervisors," she said.

Some workers from other departments joined the strike, including Miriam Camau, 28, a public health nurse who works at the site. Camau said she was surprised negotiations had deteriorated to the point of a strike, but wanted to support the social workers.

"They work so hard and I see how overwhelmed they are," she said.

Kim Chambers, 45, came to the DCFS office to fill out paperwork for her 4-year-old niece, of whom she has temporary custody. Chambers said operations seemed to be running smoothly despite the strike, but staff inside were asking people to be patient.

Chambers said she liked the striking workers' message about putting child safety first.

"I like what I see. Children should be first. They should be safe," she said.

County Executive Officer William T. Fujioka questioned the union making such a move when the two sides were close to a settlement.

“It is disappointing that they are willing to take an action that will have such a serious impact on public services when we are so close to finalizing an agreement,” he said.

Hundreds of administrators in the Department of Children and Family Services were prepared to fill in for striking workers. They will effectively perform triage, ensuring that the child-abuse hotline remains staffed, that emergency responders are available and that the agency could remain focused on “any service that might affect immediately the safety of a child,” Montiel said.

Fujioka sent a memo to all department heads Wednesday reminding them about pay and discipline policies for employee strikes or sick-outs. Employees have legal protections to strike, but are not entitled to pay, said spokesman David Sommers.

Los Angeles County social workers will strike Thursday, the first time county employees have taken to picket lines in more than a decade and a sharp escalation of a contract dispute between the county and its largest union.

UC campuses and medical centers are preparing for a one-day strike Wednesday by service workers, patient care employees and student tutors. Some elective surgeries and treatments have been postponed at the system’s hospitals and replacement workers are being hired, officials said.